1. Field of the Invention
The present invention generally relates to a recordable optical information recording medium recordable by heat mode such as CD-R, DVD-R or DVD+R, which is capable of recording and reproduction by means of, for example, a laser light having a wavelength of 350 to 830 nm, which contains a certain organic dye together with a photostabilizer such as a specific aminium compound in the recording layer, and which is capable of particularly high speed recording and also has improved light resistance.
2. Description of the Related Art
As a means for recording and reproducing image data such as characters or graphics, or video or audio data, for example, optical disks known as CD-Rs, which have a recording layer containing pentamethine-based cyanine dye, are available as the recording media capable of recording and reproduction by means of a laser light having a wavelength of 770 to 830 nm. However, it is a recent trend to use DVD-Rs (Digital Video Disk-Recordable or Digital Versatile Disk-Recordable) which are capable of high density recording and reproduction by means of a red laser light having a shorter wavelength than the aforementioned laser light, for example, in the region of 620 to 690 nm, or the like as the next-generation media (optical information recording media) to replace CD-Rs. Moreover, media recordable at even higher density, which are capable of recording and reproduction by, means of so-called blue laser having a wavelength in the order of 400 nm, are also in practical use.
In regard to such CD-R, DVD-R or DVD+R, currently recording performance is being improved by employing in the recording layer an organic dye compound which is responsive to a semiconductor laser having a wavelength of 600 to 800 nm, particularly a wavelength of 640 to 680 nm, and which forms pits by thermal decomposition or the like in accordance with the signal of the information to be recorded, thereby allowing recording. Especially, cyanine dyes and azo dyes are being widely used, since they are advantageous in that a method of high productivity called spin coating can be applied to these dyes, their low heat conductivity enables local heating and therefore formation of pits having good dimensional stability with distinct edges, and in particular, they exhibit high absorption and reflection in the region of the wavelengths of semiconductor lasers.
However, such recordable optical information recording media such as CD-R, DVD-R or DVD+R have problems that when they contain cyanine dyes or general azo dyes in the recording layer, these dyes in general cannot be said to have sufficient light resistance and are susceptible to deterioration by sunlight. Also, they may not be adequate for long-term storage of the recorded material, they are susceptible to deterioration when repeatedly irradiated with laser light upon reproduction, and are likely to impair the quality of the reproducibility of image or sound resulting from reproduction.
As a countermeasure against these problems, it has been attempted to improve the recording layer of CD-R, DVD-R or DVD+R containing cyanine dye, by adding a photostabilizer (quencher) such as a stabilized radical to the main component of the cyanine dye which in general has characteristic absorption in the region of oscillation wavelength of semiconductors, and changing the singlet oxygen, for example, generated by sunlight, which causes discoloration of the dye, to a mild triplet oxygen by way of oxidation thereof. However, when it is desired to preserve recorded material such as the content of encyclopedia for a long time, it cannot be viewed that the improvement is sufficient. Moreover, addition of such photostabilizer causes so-called thermal interference which attenuates the feature of cyanine dye or azo dye that enables local heating, has adverse effect on the recording properties, and in particular, causes deterioration of the recording sensitivity or jitter.
In particular, for the CD-R, DVD-R or DVD+R to be used in the future, in order to perform recording efficiently, it is required from the organic dye compound currently used as the dye for the recording layer to enable speeding up of recording, and thus there is an increasing demand in the market on high speed recording such as 8 times speed as well as 16 times speed recording. In such high speed recording, it is needed to perform writing by irradiating the recording layer with laser light at high speed. For this, increasing the scanning speed of the laser light is needed, and consequently the amount of energy per unit time required for the writing is to be reduced. When it is desired that good pits be formed as the signal for the information to be recorded, it is necessary either to use an organic dye having good reactivity (the ability to degrade and volatilize) which would be able to form good pits even with low energy, to design a material constitution comprising an organic dye and a photostabilizer, or to perform recording with powering up of the irradiated laser light so as to compensate for the reduction in the amount of energy, that is, with so-called formation of pits with high power, or to carry out a few of the above means in combination. In this case, addition of the above-mentioned photostabilizer to cyanine dye faces problems such as that the aforementioned thermal interference is liable to occur and light resistance is not satisfactory, and thus device on the photostabilizer is in need.
As a measure for such photostabilizer, it is disclosed in the description of the publication of JP-A-3-164292 that when a diimmonium compound in which the anionic portion is a transition metal complex is added to the cyanine dye, light resistance is significantly enhanced, as compared with the case of adding a conventional diimmonium compound in which the anionic portion is an inorganic anion instead. Further, it is disclosed in the publications of JP-A-5-148193 and JP-A-5-178808 that addition of a special aminium salt compound and a diimmonium salt (all being substituted with at least one alkoxyalkyl group or alkynyl group) to organic dye results in excellent light resistance, as compared with the case of adding a conventional diimonium salt (having none of the substituent alkoxyalkyl group or alkynyl group) instead.
However, with the recording layer formed from the aforementioned addition of an aminium salt compound or a diimonium compound (diimmonium compound) to a cyanine dye or an azo dye as the photostabilizer, it is not possible to solve the above-mentioned problem, that is, the problem that such addition is still unsatisfactory in realizing, so to speak, the conflicting performance that in order to let the recording layer cope with high speed recording, on one hand, the response of the recording layer to laser light in writing should be enhanced, while on the other hand, the response of the recording layer to any external light such as sunlight should be suppressed to suppress light-induced discoloration.